Long period exposure to serious cadmium pollution benefits an invasive plant (Alternanthera philoxeroides) competing with its native congener (Alternanthera sessilis)

Impact of trace elements on invasive plants: Attenuated competitiveness yet sustained dominance over native counterparts

Trace element pollution has emerged as an increasingly severe environmental challenge owing to human activities, particularly in urban ecosystems. In farmlands, invasive species commonly outcompete native species when subjected to trace element treatments, as demonstrated in experiments with individual invader-native pairs. However, it is uncertain if these findings apply to a wider range of species in urban soils with trace elements. Thus, we designed a greenhouse experiment to simulate the current copper and zinc levels in urban soils (102.29 mg kg-1 and 148.32 mg kg-1, respectively). The experiment involved four pairs of invasive alien species and their natural co-existing native species to investigate the effects of essential trace elements in urban soil on the growth and functional traits of invasive and native species, as well as their interspecific relationship. The results showed that adding trace elements weakened the competitiveness of invasive species. Nonetheless, trace element additions did not change the outcome of competition, consistently favoring invasion successfully. Under trace element addition treatments, invasive species and native species still maintained functional differentiation trend. Furthermore, the crown area, average leaf area and leaf area per plant of invasive species were higher than those of native species by 157 %, 177 % and 178 % under copper treatment, and 194 %, 169 % and 188 % under zinc treatment, respectively. Additionally, interspecific competition enhanced the root growth of invasive species by 21 % with copper treatment and 14 % with zinc treatment. The ability of invasive species to obtain light energy and absorb water and nutrients might be the key to their successful invasion.

Cadmium induced defense enhance the invasive potential of Wedelia trilobata under herbivore infestation

Cadmium (Cd) pollution is on the rise due to rapid urbanization, which emphasize the potential adverse effects on plant biodiversity and human health. Wedelia as a dominant invasive species, is tested for its tolerance to Cd-toxicity and herbivore infestation. We investigate defense mechanism system of invasive Wedelia trilobata and its native congener Wedelia chinensis against the Cd-pollution and Spodoptera litura infestation. We found that Cd-toxicity significantly increase hydrogen peroxide (H2O2), Malondialdehyde (MDA) and hydroxyl ions (O2•) in W. chinensis 20.61%, 4.78% and 15.68% in leave and 27.44%, 25.52% and 30.88% in root, respectively. The photosynthetic pigments (Chla, Chla and Caro) and chlorophyll florescence (Fo and Fv/Fm) declined by (60.23%, 58.48% and 51.96%), and (73.29% and 55.75%) respectively in W. chinensis and (44.76%, 44.24% and 44.30%), and (54.66% and 45.36%) in W. trilobata under Cd treatment and S. litura. Invasive W. trilobata had higher enzymatic antioxidant SOD 126.9/71.64%, POD 97.24/94.92%, CAT 53.99/25.62% and APX 82.79/50.19%, and nonenzymatic antioxidant ASA 10.47/16.87%, DHA 15.07/27.88%, GSH 15.91/10.03% and GSSG 13.56/17.93% activity in leaf/root, respectively. Overall, W. trilobata accumulate higher Cd content 55.41%, 50.61% and 13.95% in root, shoot and leaf tissues respectively, than its native congener W. chinensis. While, nutrient profile of W. chinensis reveals less uptake of Fe, Cu and Zn than W. trilobata. W. trilobata showed efficient alleviation of oxidative damage through upregulating the genes related to key defense such as SOD, POD, CAT, APX, GR, PROL, FLV, ABA and JAZ, and metal transporter in leaves, shoot and root tissues, respectively. Conclusively, W. trilobata efficiently employed Cd-triggered defense for successful invasion, even under S. litura infestation, in Cd-contaminated soil.

Microplastics and cadmium affect invasion success by altering complementarity and selection effects in native community

The diversity-invasibility hypothesis predicts that native plant communities with high biodiversity should be more resistant to invasion than low biodiversity communities. However, observational studies have found that there is often a positive relationship between native community diversity and invasibility. Pollutants were not tested for their potential to cause this positive relationship. Here, we established native communities with three levels of diversity (1, 2 and 4 species) and introduced an invasive plant [Symphyotrichum subulatum (Michx.) G. L. Nesom] to test the effects of different pollutant treatments (i.e., unpolluted control, microplastics (MPs) alone, cadmium (Cd) alone, and their combination) on the relationship between native community diversity and community invasibility. Our results indicate that different MPs and Cd treatments altered the invasibility of native communities, but this effect may depend on the type of pollutant. MPs single treatment reduced invasion success, and the degree of reduction increased with increasing native community diversity (Diversity 2: - 14.1 %; Diversity 4: - 63.1 %). Cd single treatment increased the aboveground biomass of invasive plants (+ 40.2 %) and invasion success. The presence of MPs inhibited the contribution of Cd to invasion success. Furthermore, we found that the complementarity and selection effects of the native community were negatively correlated with invasion success, and their relative contributions to invasion success also depended on the pollutant type. We found new evidence of how pollutants affect the relationship between native community diversity and habitat invasibility, which provides new perspectives for understanding and managing biological invasions in the context of environmental pollution. This may contribute to promoting the conservation of biodiversity, especially in ecologically sensitive and polluted areas.

Soil cadmium pollution facilitated the invasion of alligator weed through enhanced herbivore resistance and competitive ability over a congeneric species

A number of invasive plant species, such as Alternanthera philoxeroides, have been documented to be able to accumulate trace metal elements in their tissues. Since metal accumulation in plants can serve as a defence against herbivores, we hypothesized that metal pollution will increase herbivore resistance of metal-accumulating invasive plant species and such a benefit will grant them a competitive advantage over local co-occurring plants. In this study, we compared the differences in plant growth and herbivore feeding preference between A. philoxeroides and its native congener Alternanthera sessilis in single and mixed cultures with and without soil cadmium (Cd) pollution. The results showed that A. philoxeroides plants were more tolerant to Cd stress and accumulated more Cd in the leaves than A. sessilis. Cd exposure increased the resistance of A. philoxeroides against a specialist and a generalist herbivore compared with A. sessilis. Competition experiments indicated that Cd stress largely increased the competitive advantage of A. philoxeroides over A. sessilis with or without herbivore pressures. The differences in herbivore resistance between the two plant species under soil Cd stress are most likely due to the deterring effect of Cd accumulation and Cd-enhanced mechanical defences rather than changes in leaf specialized metabolites.

Heavy metal induced resistance to herbivore of invasive plant: implications from inter- and intraspecific comparisons

Introduction

Heavy metals can affect the content of secondary metabolites in plants, which are one of the important defenses of plants against herbivores. However, studies on the effects of heavy metals on secondary metabolites of invasive plants are scarce. Phytolacca americana is an invasive plant in China, which can hyperaccumulate the heavy metal Mn.

Methods

This study used two Mn treatments (control and treatment group) and four species from Phytolacca (including the native and introduced populations of P. americana, its native and exotic congeners in China) to investigate the impact of heavy metal Mn on the invasive ability of P. americana.

Results

The results show that heavy metal Mn can enhance the inhibitory effect of the introduced populations of P. americana on the growth of herbivore (the weight of herbivore has decreased by 66%), and altered the feeding preferences of herbivore. We also found that heavy metal Mn can significantly increase the content of quantitative resistance in the leaves of the introduced populations of P. americana and is higher than its native populations, native and exotic congeners. In addition, heavy metal Mn caused the quantitative resistance of the exotic congener significantly higher than that of the native congeners.

Discussion

In summary, the heavy metal Mn can increase the content of secondary metabolites in leaves to enhance the interspecific competitive advantage of P. americana and promote its invasion, and also increase the invasion risk of exotic species.

Invasive Plant Alternanthera philoxeroides Benefits More Competition Advantage from Rhizosphere Bacteria Regardless of the Host Source

The rhizosphere plays a vital role in the exchange of materials in the soil-plant ecosystem, and rhizosphere microorganisms are crucial for plant growth and development. In this study, we isolated two strains of Pantoea rhizosphere bacteria separately from invasive Alternanthera philoxeroides and native A. sessilis. We conducted a control experiment to test the effects of these bacteria on the growth and competition of the two plant species using sterile seedlings. Our findings showed that the rhizobacteria strain isolated from A. sessilis significantly promoted the growth of invasive A. philoxeroides in monoculture compared to native A. sessilis. Both strains significantly enhanced the growth and competitiveness of invasive A. philoxeroides under competition conditions, regardless of their host source. Our study suggests that rhizosphere bacteria, including those from different host sources, can contribute to the invasion of A. philoxeroides by significantly enhancing its competitiveness.

Neutral-to-positive cadmium effects on germination and seedling vigor, with and without seed priming

This review gathered and analyzed data about (i) the Cd-induced impacts on seed germination and seedling vigor, and (ii) the use of different priming agents to mitigate Cd-induced impacts on the early plant development. Critical evaluation of the obtained data revealed intriguing results. First, seeds of diverse species can endure exposures to Cd. Such endurance is exhibited as maintenance of or even improvement in the seed germination and vigor (up to 15% and 70%, respectively). Second, the main factors influencing seed tolerance to Cd toxicity are related to temporal variations in anatomical, physiological, and/or biochemical features. Third, Cd can trigger diverse transgenerational effects on plants by shaping seed endophytes, by modulating seed provisioning with resources and regulatory elements, and/or by altering seed (epi)genomics. Fourth, different chemical, biological and physical priming agents can mitigate Cd-induced impacts on seeds, sometimes enhancing their performance over the control (reference) values. Overall, this review shows that the impacts of Cd on seed germination and vigor encompass not only negative outcomes but also neutral and positive ones, depending upon the Cd dose, media properties, plant species and genotypes, plant developmental stage and organ, and management approaches. Increasing our understanding of plant tolerance mechanisms against the growing background Cd pollution is relevant to support breeding programs, agricultural practices, and health-environmental policies.

Latitudinal trends in the structure, similarity and beta diversity of plant communities invaded by Alternanthera philoxeroides in heterogeneous habitats

Variations in latitudinal gradients could lead to changes in the performance and ecological effects of invasive plants and thus may affect the species composition, distribution and interspecific substitution of native plant communities. However, variations in structure, similarity and beta (β) diversity within invaded communities across latitudinal gradients in heterogeneous habitats remain unclear. In this study, we conducted a two-year field survey along 21°N to 37°N in China, to examine the differential effects of the amphibious invasive plant Alternanthera philoxeroides on native plant communities in terrestrial and aquatic habitats. We compared the differences in the invasion importance value (IV), species distribution, community similarity (Jaccard index and Sorenson index) and β diversity (Bray-Curtis index and β_sim index) between terrestrial and aquatic communities invaded by A. philoxeroides, as well as analyzed their latitudinal trends. We found that the IV of A. philoxeroides and β diversity in aquatic habitats were all significantly higher than that of terrestrial, while the terrestrial habitat had a higher community similarity values. The aquatic A. philoxeroides IV increased with increasing latitude, while the terrestrial IV had no significant latitudinal trend. With increasing latitude, the component proportion of cold- and drought-tolerant species in the terrestrial communities increased, and the dominant accompanying species in the aquatic communities gradually changed from hygrophytes and floating plants to emerged and submerged plants. In addition, the aquatic communities had lower community similarity values and higher β diversity in higher latitudinal regions, while terrestrial communities had the opposite parameters in these regions. Our study indicates that the bioresistance capacities of the native communities to invasive A. philoxeroides in heterogeneous habitats are different; A. philoxeroides invasion leads to higher community homogenization in terrestrial habitats than in aquatic habitats, and terrestrial communities experience more severe homogenization in higher latitudinal regions. These findings are crucial for predicting the dynamics of invasive plant communities under rapid global change.

Effects of simulated acid rain on rhizosphere microorganisms of invasive Alternanthera philoxeroides and native Alternanthera sessilis

Acid rain not only has serious harm to the environment, but also has the same threat to plants, but the invasive plant Alternanthera philoxeroides still grows well compared to the native plant Alternanthera sessilis under acid rain stress. However, the underlying mechanism of resistance to the acid rain environment in invasive Alternanthera philoxeroides remains unclear. In the current study, we comparatively analyzed the plant physiological characteristics, soil physicochemical properties, and rhizosphere microbial communities of invasive A. philoxeroides and native A. sessilis under different pH condition. The simulated acid rain had a significant inhibitory effect on the morphological and physiological traits of A. philoxeroides and A. sessilis and reduced the soil nutrient content. However, A. philoxeroides was more tolerant of acid rain. Compared with CK, simulated acid rain treatment at pH 2.5 significantly increased the Chao1, ACE, and Shannon indexes of A. philoxeroides microorganisms. Under simulated acid rain treatment at pH 2.5, the fungal flora Chao1, ACE and Shannon index were significantly higher than those of CK by 14.5%, 12.4%, and 30.4%, respectively. The dominant bacterial phyla of soil bacteria were Proteobacteria, Actinobacteria, Bacteroidota, Actinobacteria, Firmicutes, Myxococcota, Chloroflexi, Patescibacteria, Gemmatimonadota, Verrucomicrobiota, and Armatimonadota. The dominant fungi were Ascomycota, Basidiomycota, Rozellomycota, and Olpidiomycota. The bacterial and fungal diversity and structure of A. philoxeroides and A. sessilis showed the greatest difference between the pH 2.5 treatment and CK. Redundancy analysis showed that electrical conductivity (EC) and total phosphorus (TP) were the main factors changing the bacterial communities, and available phosphorus (AP), organic matter (OM), EC, and pH were the main factors changing the fungal communities. This study contributes to the microbial community structure of the invasive plant A. philoxeroides and provides a theoretical basis for studying the invasion mechanism of invasive plants under acid rain.

Effect of Acid–Base Modified Biochar on Chlortetracycline Adsorption by Purple Soil

We used three purple soil (Hechuan, Jialing, and Cangxi) samples from the Jialing River basin as the research objects and added different proportions of an acid–base modified Alternanthera philoxeroides biochar (Cm) to the purple soil to study the effect of Cm on the adsorption of chlortetracycline (CTC) in the purple soil. The results indicated the following: (1) At 30 °C and pH = 6, the soil adsorption capacity increased with an increasing initial concentration of CTC. The maximum adsorption amount of CTC for each tested sample was in the range of 2054.63–3631.21 mg/kg, and the adsorption capacity in different Cm amended soils was ranked in the order of 10% Cm > 5% Cm > 2% Cm > CK. The adsorption capacity of CTC increased with an increase in the proportion of Cm. Furthermore, under the same addition ratio of Cm, Hechuan soil was found to have a better adsorption effect for CTC than Jialing and Cangxi soil. (2) The Langmuir model was the most suitable for fitting the adsorption behavior of CTC on different purple soils, and the fitting coefficients were all greater than 0.9, indicating that the adsorption of CTC on each soil sample occurred via monolayer adsorption. The thermodynamic experiment results showed that an increase in temperature was beneficial to the process of CTC adsorption, which was a spontaneous, endothermic, and entropy-adding process. (3) At pH = 6, the ionic strength ranged from 0.01 to 0.5 mol/L and the adsorption capacity of CTC of the soil samples decreased with an increase in ionic strength. In the range of pH 2–10, the adsorption capacity of CTC in all the soil samples decreased with an increase in pH. The inhibition capacity of CTC in the soil samples under acidic conditions was notably higher than that under alkaline conditions.

The rapid evolution of an invasive plant due to increased selection pressures throughout its invasive history

Invasive plants are highly successful because they can quickly adapt to selection pressures imposed by both biotic and abiotic stressors. Since selection pressures may vary across temporal and biogeographical gradients, the growth and fitness of invasive plants varies across time. However, only a few studies have focused on the evolutionary potential of invasive plants following their establishment. In this study, the impacts of cadmium (Cd) on the germination and seedling growth of an invasive plant, Ageratina adenophora, were examined. The seeds were collected from different historical populations at the invasion stage (during the early, middle, and new stages of invasion). Plant performance was tested under both heavy metal and simulated herbivory treatments to examine the evolution of A. adenophora under different selection pressures. It was found that early stage A. adenophora populations have higher germinability and weaker seedling growth than the new stage populations. Compared with new stage populations, early-stage populations are more tolerant to simulated herbivory and their germination potential tends to be higher under high Cd stress. It seems that the adaptive strategy of A. adenophora is to invest more energy in growth during the initial stage of invasion. As selection pressures increases over time, more energy seems to be shifted to the improvement of seed quality as well as to the vegetative growth system which improves its ability to tolerate stressful environments. It is important to consider the invasion history of a species when studying the invasive and evolutionary potential of plant species.